The field of the invention relates to electromagnetic fuel injectors, fuel rails and processes for fabricating same.
For motor vehicle applications in particular, it is known to mechanically couple a plurality of electromagnetic fuel injectors between a fuel rail and an intake manifold of an internal combustion engine. In response to an electronic drive signal, the actuated fuel injector passes fuel from the fuel rail into the intake manifold for a predetermined time thereby delivering a predetermined amount of fuel. For accurate fuel delivery, each fuel injector coupled to the fuel rail must deliver substantially the same amount of fuel during the predetermined time of actuation.
A typical fuel injector, which is illustrated herein in Prior Art FIG. 1, is shown connected to fuel rail 102 by fuel connector 6. Fuel injector 10, which is one of a plurality of fuel injectors connected to fuel rail 4, includes housing 12 constructed of an electromagnetic permeable material and having a lower housing 14 crimped to an upper housing 16. Lower housing 14 is fabricated by a conventional cold heading and machining process which forms fuel passageway 18 and cavity 20 for receiving coil bobbin assembly 22 therein Electrical contacts 24 are positioned through plastic cap 26 and connected to coil bobbin assembly 22 through housing 12. Placement of "O" ring 28 and "O" ring 30 on respective lower housing 14 and upper housing 16 within cavity 20 is required to seal coil bobbin assembly 22 and electrical contacts 24 from fuel passageway 18.
Continuing with Prior Art FIG. 1, armature 34 is slidably, axially mounted within fuel passageway 18 and biased against spring 32. Armature 34 is connected to stem 36 which is axially positioned within sleeve 42 and includes conical end 38. Lower housing 14 is crimped to sleeve 42. Sleeve 42 has a conical seat 46 formed around valve opening 50 for mating with conical end 38 of stem 36 thereby forming a needle and seat valve. Fuel passageway 18 communicates with sleeve 42 and extends through upper housing 16 to fuel connector 6 which mates with fuel rail 4.
During operation, coil bobbin assembly 22 is electrically actuated by a drive signal of predetermined voltage and pulse width. A magnetic field is thereby induced through a magnetic core defined by lower housing 14 and upper housing 16. This induced magnetic field couples to armature 34 deflecting it against spring 32 thereby opening the needle and seat valve. When the drive signal is deactuated, spring 32 downwardly deflects armature 34 thereby closing the needle and seat valve. Accordingly, dynamic fuel flow through the fuel injector is related to spring strength of spring 32, electrical characteristics of coil bobbin assembly 32, and size of valve opening 50.
Prior approaches have also sought to separately adjust fuel delivery through each fuel injector and match sets of fuel injectors to a fuel rail. More specifically, tube 56 is inserted within fuel passageway 58 against spring 32 of prior art fuel injector 12 or similar fuel injector. Fuel injector 12 is then inserted on a test stand (not shown) and tube 56 connected to a stepper motor (not shown) for coupling axial movement to tube 56. A fuel metering probe (not shown) is coupled to fuel passageway 58 which in turn is coupled to a source of pressurized fuel (not shown). A voltage signal is then applied to electrical contacts 24 for a predetermined time and fuel flow measured. Tube 56 is axially displaced, upwardly or downwardly, until a desired fuel flow is measured during such predetermined time. Afterwards, tube 56 is crimped to prevent further movement. In effect, the spring constant of spring 32 is being adjusted to achieve a desired dynamic response. In accordance with the test measurements, a set of closely matched fuel injectors are selected for installation on a particular fuel rail.
The inventor herein has recognized numerous disadvantages of the prior art device and processes described above. For example, the fuel adjusting and fuel injector matching processes have inherent inaccuracies in addition to manufacturing complexity. A number of test stands are required for efficient manufacturing and each of these stands is calibrated differently. Accordingly, there will be variances between fuel injectors processed on different stands. Further, the measuring probe influences fuel flow through each injector such that the resulting measurements may not accurately reflect actual fuel flow. In addition, only the injectors are adjusted and measured, fuel flow variances are also introduced by the fuel rail.
The inventor herein has also recognized numerous disadvantages of the prior art structural devices, specifically the fuel injector and fuel rail. Numerous processing and assembly steps are required to fabricate a fuel rail and couple each individual fuel injector to the fuel rail through a corresponding fuel connector. Further, for each fuel injector, several "O" rings and corresponding assembly steps are required to seal coil bobbin assembly 22 and electrical contacts 24 from fuel passageway 18. In addition, complicated processing steps are required such as cold heading and machining lower housing 12 to form fuel passageway 18 and cavity 20. Cumbersome crimping steps are also required to assemble lower housing 12 to upper housing 14 and sleeve 42. The magnetically permeable housing is also susceptible to corrosion in typical under hood environments.